Polyurethane Ink Dispersion Prevents Nozzle Clogging
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Solution Overview
Problem
Current inkjet inks face challenges in achieving long shelf life and efficient curing, particularly when thermal curing is required without stabilizers, and radiation curing is not always feasible due to geometry constraints, leading to issues with nozzle clogging and print stability.
Innovation Solution
Aqueous dispersions of pigments partially enveloped by a specific polyurethane, comprising di- or polyisocyanates with allophanate groups and isocyanate-reactive compounds, along with a polymerization inhibitor, which allows for both actinic and thermal curing while maintaining stability and preventing nozzle clogging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If thermal curing is used without stabilizers, then curing efficiency is improved, but shelf life deteriorates due to premature polymerization
Solution Approach 1:
A polymerization inhibitor is added to the ink formulation before use to prevent premature polymerization during storage. The inhibitor acts as a preliminary protective measure that maintains stability during storage but can be removed or deactivated during the curing process, allowing efficient thermal curing when needed.
Solution Approach 2:
The polymerization inhibitor serves as an intermediary substance that mediates between the conflicting requirements of stability during storage and reactivity during curing. It temporarily suppresses polymerization activity during storage but does not permanently prevent curing, allowing both requirements to be satisfied at different stages.
2Speed
If radiation curing is used, then curing speed is improved, but adaptability deteriorates due to geometry constraints of radiation sources
Solution Approach 1:
The invention provides the option to switch between different curing methods (thermal or radiation) depending on the application requirements. This dynamic approach allows optimization of curing speed when using radiation for suitable substrates, while maintaining adaptability to non-planar substrates by using thermal curing when needed.
3Illumination intensity
If dispersed colorant particles are used, then color brilliance is improved, but reliability deteriorates due to nozzle clogging
Solution Approach 1:
The ink formulation uses specific parameter optimizations including controlled particle size distribution of dispersed colorants, optimized viscosity, and appropriate surfactant concentrations. These parameter changes allow the ink to maintain color brilliance while reducing the tendency of particles to aggregate and clog nozzles during storage and printing.
Solution Approach 2:
Surfactants and dispersants act as intermediary substances that coat the dispersed colorant particles, preventing them from aggregating and adhering to nozzle surfaces. These intermediaries maintain the benefits of dispersed colorants for color brilliance while protecting against the harmful effect of nozzle clogging.
4Ease of manufacture
If pigment particles are dispersed in aqueous medium, then processability is improved, but stability deteriorates due to sedimentation
Solution Approach 1:
The ink formulation optimizes several parameters including pH control, ionic strength, surfactant concentration, and particle size distribution. These parameter changes create a stable colloidal system where pigment particles remain dispersed in the aqueous medium during storage, preventing sedimentation while maintaining good processability for printing applications.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution provides inkjet inks with improved shelf life and curing capabilities, ensuring stable prints with high dry rub, light, and water fastness, and preventing nozzle clogging, even on non-planar substrates.
Implementation Method 1
Such inks, in contrast, have a limited shelf life in some cases... aqueous dispersions... further comprising at least one polymerization inhibitor (C)
Implementation Method 2
Radiation-curable ink jet inks typically comprise a material which can be cured by subjecting it to actinic radiation
Implementation Method 3
Thermal curing of the inks disclosed in WO 2006/089933, however, is possible in those cases only
Data Source
AI summary
The present invention provides aqueous dispersions comprising a pigment (B) at least partially enveloped by polyurethane (A) and further comprising at least one polymerization inhibitor (C), said polyurethane (A) being obtainable by reaction of(a) 15% to 70% by weight of di- or polyisocyanate comprising on average from 1 to 10 allophanate groups and on average from 1 to 10 C—C double bonds per molecule, and optionally(b) 0% to 60% by weight of further di- or polyisocyanate, with(c) 5% to 50% by weight of compound having at least two isocyanate-reactive groups,weight % ages being based on total polyurethane (A).